There are a variety of electrical system applications, which require one or more sources of high voltage AC power. As a non-limiting example, a liquid crystal display (LCD), such as that employed in desktop and laptop computers, or in larger display applications such as large scale television screens, requires an associated set of cold cathode fluorescent lamps (CCFLs) mounted directly behind it for backlighting purposes. In these and other applications, ignition and continuous operation of the CCFLs require a high AC voltage that can range on the order of several hundred to several thousand volts. Supplying such high voltages to these devices has been customarily accomplished using one of several methodologies.
A first approach involves the use a single-ended drive system, wherein a high voltage AC voltage generation and control system is transformer-coupled to one/near end of the lamp. This approach requires the generation of a very high peak AC voltage in the high voltage transformer circuitry feeding the driven end of the lamp.
Another approach is to generate double-ended drive with all switches and transformers placed close to one end of the lamp and high voltage coupled to both the near end and the far end with high voltage wire. These wires can be relatively long (e.g., 4 feet or more) and are more expensive than low voltage wires due to their high voltage insulation. In addition, they loose significant energy through capacitive coupling to ground.
Another approach is to place a high voltage transformer and associated voltage switching devices, such as MOSFETs or bipolar transistors, at both the near end and the far end of the lamp; these devices are connected to and controlled by a local controller at the near end of the lamp. This approach has disadvantages similar to the first, in that the gate (or base) drive wires are required to carry high peak currents and must change states at high switching speeds for efficient operation. The long wires required are not readily suited for these switching speeds, due to their inherent inductance; in addition they lose energy because of their substantial resistance.
An alternative and safer approach has been to drive the respective ends of the lamp with opposite phase AC voltages. For this purpose, a full control system including respective high voltage transformers, drivers and associated switching systems therefore may be installed at each end of the lamp, and being operative to drive near and far terminals of the lamp with equal and opposite AC voltages. This approach has the advantage that the drive voltages supplied to the opposite ends of the lamp may be reduced to half that of a single ended system. However, it adds complexity to the circuitry at the remote end of the lamp, and additionally requires interconnections between the two systems to synchronize the frequency and phase of each driver, as well as other functions such as brightness control.